What is it?

The J1772 Hydra is a two headed J1772 electric vehicle charging station. There are two board variants. One is a standalone charging station that plugs in (or is hardwired) into a standard 208/240 volt electric circuit. The other has a J1772 inlet and can be used to share an existing J1772 charging station with two vehicles.

The Hydra has two operating modes. In the "Sharing" mode, when both cars request power, each is given 50% of the available power. When one car finishes, the other car is boosted up to 100% power. In the "Sequential" mode, one car is given 100% power until it finishes, and then the other car is given an opportunity to charge.

The EVSE variant includes a real-time clock and timer system - particularly helpful for two EV households that have time-of-use electric metering. You can charge both cars overnight without switching the plug in the middle of the night!

The splitter variant is intended to be used to share charging stations that are already installed and operating. It can be configured with separate power (120/208/240VAC 50/60Hz) so that the host EVSE is only turned on when a car wants power, or it can be configured to obtain power from the host EVSE (turning it on immediately on connection).

Both Hydras operate in full compliance with the J1772 and all relevant safety standards. The EVSE variant includes a ground-fault detector, and both variants include a ground impedance testing and stuck relay detection system. Both variants also include ammeters to insure that neither car draws more power than it is allowed at any given moment (and to show how much current each car is drawing). The firmware of the Hydra insures that the available current (either as indicated by a host EVSE for the splitter variant, or as configured by the installer for the EVSE variant) is never exceeded.

The heart of the hydra is two PCBs - an HV / power board that has all of the high voltage components, and a logic/display board with the rest of the circuitry. An FFC cable connects the two.

NOTE

This item is just the two circuit board assemblies. To build a complete Hydra, you must add a chassis/enclosure, two two-pole contactors, two J1772 cable/plug sets, two current transformers, a power distribution manifold and and a number of other wiring components and cabling. See the documentation for a full rundown on what you need. The Hydra boards assemblies themselves are fully assembled, so the rest of the construction requires no soldering.

Why did you make it?

I leased an EV because there were charging stations at the office and the idea of having half my commute expenses paid for by the company was attractive. Unfortunately, the charging stations were oversubscribed, and a great number of users were cars that charged at 3.3kW - effectively only using half of available power of the charging station. The J1772 Hydra was born to allow the charging stations to be fully utilized. Later, we leased a second EV, and I created the EVSE variant to allow us to charge both of them at once without having a separate "host" EVSE.

What makes it special?

To my knowledge, the J1772 Hydra remains unique. It's the only solution to seamlessly share a J1772 charging station with two cars while still remaining fully compliant with the J1772 specification and all relevant safety standards, and one of only two available double-headed, single circuit charging stations (and the other one is intended for public, commercial installations).

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Review Breakdown

Average Ratings

Good project with little to no alternatives at the moment

If you have two electric cars, you need something like this to lead a normal life.

By the moment of this writing, i have been using Hydra to charge my cars for 3.5 months, and i am as happy as can be.

There are not many options in that case. The simplest one is to install 2 chargers on 2 breakers. That might not be possible (as it was not for me), as it adds to loads on the panel -- one may run out of capacity both amperage and space wise.

Then, one might try and find dual head chargers on one breaker. Not many at all as far as residential options are concerned, and they all cost a little fortune (we are getting into double digits of a percentage of the car cost itself!). Given the standards seem to move pretty fast, this does not look like a good expense at all.

And there are absolutely none that one could just plug in.

Hydra has it all -- and it does it in a very compact package. Ability to run shared and sequential modes in residential settings are superb and are exactly what one needs to keep things running smoothly. TOU scheduling is present (I actually extended it to 5 events to accomodate half-peak options of my tariff).

There are a few things that add to the cost though: (a) one needs to be ready to mess with the assembly process. This requires time, tools, and some experience. That said, if you build your own computers like I do, this should not be a great problem (assuming the process of assembly is well understood).

(b) Bill of materials could be better. There are less expensive alternatives and suppliers on the list. Some little things might be mentioned (like e.g. hanging tabs for the poly case -- if you don't order them at the same time, that's 2x shipping charge on a separate order for a very small accessory). Packard contactors @ open evse store can be used, but i ended up using these ones (they were @ $9 apiece at Amazon at that time) -- they are also compatible: https://www.amazon.com/gp/product/B01J4Z8SZU. I bought a lot from amazon; but mounting hardware seems to be better bought @ digikey, along with a few other components.

(c) There may be a few bugs.

The PCBs by OshPark are not QA'd, i had a missing path on mine, which was not obvious until i went back to Nick to analyze it. Luckily, I lived not so far from him. Otherwise, it would've been pretty hard to figure out if it was my mistake or faulty PCB's or something entirely else. I don't have necessary expertise for this kind of trouble shooting. Sequential mode was broken in the latest firmware, i had to fix it and a few other things, i PR'd the updates to Nick's github.

(d) Documentation was generally easy to follow, but I see how first time experience may lead to a wiring error, which is especially something you don't want to do with the HV componentry.

(e) Design: there are limitations. Two major features that are missing in comparison to modern EVSEs are wifi with cloud analytics (or a phone app of the same), and temperature throttling. I do not care much for the analytics (my Tesla app is going to tell me everything i need to know), but the temperature throttling is an important monitoring and safety feature IMO. Open EVSE has been having it for years now; so is the L1 EVSE that came with my car. I am planning to implement temperature throttling addition to the firmware as soon as i get a Hydra version with an I2C header to connect one of the cheaper sensors found on Amazon. That should be easy enough. I found that a spurious false ground fault error may occur that would prevent cars from completing the charge process. Open EVSE apparently has this issue too, so they added a feature that would automatically attempt to restart the charging up to 4 times. I added that feature, among a few others, in the latest Hydra patch as well.

Conclusion: this is an excellent design, customizable as well, but one should be keenly aware that like all DIY projects, this is not exactly a plug-and-play project.

Awesome product, superb support, a bit confusing

We've been a 2 EV family for 2 years now but only have a single charging station in the garage. Most of the time the first car (with a 6.6kW charger) was done in less than 2 hours so it was a simple matter of swapping the cable (if I remembered) before bed. But we traded my wife's 6.6kW LEAF for a Volt recently, and that car charges SLOWLY, as does my older 3.3kW LEAF. That meant I would sometimes have to wait up for her car to complete so I could swap the cable. And if we both arrived home late, that usually meant getting the 120V charger out and hoping it would finish by morning. The J1772 Hydra is the perfect solution for us.

Altogether in parts it's quite an investment, as the developer warns. But for us, it worked out about the same as getting a second charging station (which actually would've been difficult since our panel couldn't accept another 240V circuit as is), and having a portable unit that I could take anywhere if I needed to was a win.

The project got off to a slow start as the initial shipping was delayed, but Nick more than made up for it in support and excellent response from that point on.

The board itself seems very well designed, and is being actively developed. Nick has had extensive experience with the OpenEVSE project, so I trust that he knows the ins and outs of charging stations. I have a high confidence in the design and Nick's support. While I chose to go "by the book" as far as the external components and configuration goes, there is sufficient information provided if you want to tweak the design to your specifications (both from a hardware and software perspective).

The main issue I had (aside from the fact that I'm a chip designer by trade, so working with high voltage components is quite foreign to me) is that with all the development activity and revs to the board, referencing the correct documentation is a challenge. Going into the project I found two different build documents (one for an older rev and one for what looked like the current rev), plus an illustrated build guide, plus a software repository, all spread around different sites. And even then, as I later found out, I was not referencing the most recent documentation which was on yet another site. As it turned out, referencing back-level documentation is a big problem, so make 100% sure you are referencing the current docs. I just checked and the current docs ARE linked from this site (and you should probably check with Nick just in case). In my case, my initial web search for the J1772 Hydra (since I was aware of its name) found the obsolete docs first (which I didn't know were obsolete at the time) and those had a link to this store which I just quickly ordered the board from without checking the documentation link.

I will say that the older docs are actually better in some respects. The instructions are a bit more detailed in some key areas. But on the other hand, the newer instructions have a more complete/succinct BOM list (something that would have helped me tremendously), and most importantly they are current!

As for the BOM list, as I mentioned, the current docs have a more complete BOM list, but it's not necessarily better. While the older docs had incomplete BOM lists, and they were spread around the documentation, I will say that the older docs did a better job at identifying potential sources for the parts. The current docs ALMOST do this, but not quite. For example, the older docs had a much better discussion on where to get the J1772 cable sets and things to watch out for when it came to making sure the proximity sensor wires in the cable actually did something. For the record, I was able to get what I feel was a high quality cable for the best price from Quick Charge Power, although even then I had to hack the nozzles a bit to get the proximity wire hooked up (something the old docs mentioned, but the newer ones don't cover at all). Nick also referred me to good sources for some of the other components. Examples: the best deal on the contactors was from OpenEVSE.com, whereas the button was a better deal from Adafruit (although if you are already ordering from OpenEVSE, you could save shipping costs by buying from them).

So I had three major issues with the build. First, one of the two boards included in this project had a defect. Nick gladly sent out replacement boards even before I returned the defective board. This was excellent service. The other two issues were mine. The first of those is that because I was referencing older docs, I got the wrong contactors and actually damaged the HV board, which again, Nick gladly replaced and even helped me to diagnose and get back up and running. The other is that once I had the correct contactors, I hooked them up wrong. Again, this could have been avoided by pointing to the most recent docs. Fortunately the only damage I did this time was to the contactors themselves. Thankfully the contactors at OpenEVSE are only $12 compared to about $47 from Grainger!

The build itself did take quite a bit of time (and significantly more considering I actually built/rebuilt the unit 4 times due to my errors!) but most of that was in getting parts and realizing I didn't have everything I needed. The older docs failed to mention some items which a hobbyist might have on hand (but I didn't), so I had to go back and order more supplies. The current docs do have a better list. I will say that while intimidating at first, the project is actually quite straightforward to wire up and Nick has done a fine job in creating a nice, compact arrangement for mounting. My only critique here is that I would probably find a way to mount the components such that both the outlets come out of the bottom of the case, and the inlet on the side (perhaps even rotating the case to a "landscape" orientation). I mounted my inlet in such a way that the angled nozzle was "sideways", and that way I could hang the finished project flush against the wall, but this seems kind of kludgy--a side mounted inlet would solve this problem. AND, having the outlet cables come out of the bottom would seem a little better from a mounting standpoint. But as it is, there is nothing functionally wrong with it and it works fine. The cables and inlet I got had smaller gauge pairs of wires (rather than single thicker gauge). This made it easier for me to route the wires than the unit described in the instructions. I think this would also have afforded me the opportunity to have a tidier cable routing (with somewhat longer wires) and properly cable tie them.

In the end, and with excellent support from Nick, I was able to get my J1772 Hydra working great. It can charge both my cars simultaneously (since they both only pull a maximum of 15A), but there is a sequential mode available (to charge one after the other), and if I did have a 30A capable vehicle, the unit should slow that vehicle down while a second vehicle is charging. It's really a great solution!

If you can financially justify the expense of the additional hardware required for this project, I would highly recommend this for someone with 2 EVs, or even someone that regularly charges in public where charging stations are limited.

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